Biodegradable and conductive chitosan–graphene quantum dot nanocomposite microneedles for delivery of both small and large molecular weight therapeutics

Abstract

Chitosan–graphene quantum dot nanocomposites are used in microneedle arrays for transdermal delivery of small and large molecular weight drugs.

Photoluminescent and superparamagnetic reduced graphene oxide–iron oxide quantum dots for dual-modality imaging, drug delivery and photothermal therapy

“…Here, excitation of the MGQDs at 320 nm (corresponding to the peak in the excitation spectrum) yields an emission spectrum with a peak at 398 nm. This emission value is slightly lower than that (420 nm) observed for the GQDs prepared by the same hydrothermal method [40]. Quantum yield measurements (using Equation 1) gave a value of 7.9% for the MGQDs, similar to the published literature for GQDs (5.5-14%) prepared by other groups [20,23,24,75] and slightly lower than the GQDs prepared using the same method (9.4%) [40].…”

“…The diameter of the MGQDs is larger than hydrothermally reduced GQDs (5-25 nm) previously reported by by other groups [25,38,39], but these papers use either a longer hydrothermal treatment time (24 h) [38,39] or an additional oxidation procedure to further reduce the size of their GO before the hydrothermal treatment [25]. The diameter is, however, similar to that of the GQDs (51.9 nm) prepared by the same oxidation and hydrothermal treatment method in our group [40]. The MGQDs are identifiable in both the conventional and high resolution TEM images in dark contrast ( Figure 2A1-2A2, 3A) on the amorphous carbon film support due to the presence of high density IO (4.9 -5.2 g cm -3 for magnetite [41]) within the MGQDs as well as mass-thickness contrast, similar to the identification of IO on GO-IO reported in the literature [9].…”

“…This emission value is slightly lower than that (420 nm) observed for the GQDs prepared by the same hydrothermal method [40]. Quantum yield measurements (using Equation 1) gave a value of 7.9% for the MGQDs, similar to the published literature for GQDs (5.5-14%) prepared by other groups [20,23,24,75] and slightly lower than the GQDs prepared using the same method (9.4%) [40]. These suggest the presence of IO slightly quenches the luminescence of GQDs.…”

“…MGQDs, in a 1 mg ml -1 aqueous suspension, have a PL lifetime of 1.9 ns ( Figure 5C), similar to GQDs and conventional QDs in the literature (range of 1-10 ns) [76][77][78][79], and slightly lower than the GQDs prepared using the same method (2.3 ns) [40]. Previously reported GQDs with attached IO (GQD-IOs) did not possess PL properties as they synthesized GQDs first and then attached IO [15].…”

“…As described previously, the average thickness of the MGQDs from AFM is 2.3 nm, which is thicker than the reported thickness of graphene (0.37 nm [46]), rGO (~0.8 nm [47]) or the GQDs prepared using the same hydrothermal reduction method (1.5 nm [40]). This suggests that the IO coating on both sides of the MGQD surface is likely 0.8 -1.9 nm thick; however, we do not exclude the possibility of the presence of some residual thicker nanoparticles in the MGQD.…”